After the federal prosecutors said authorities had conducted searches in connection with a second spying case, Chancellor Angela Merkel's coalition partners said on Wednesday that Washington should remove any US embassy staff involved and cease spying on its ally.

Security sources told Reuters the latest suspect to face investigation was from the military and worked in the Defense Ministry in Berlin, but no arrest appeared to have been made. Other sources close to the investigation said the suspect was a German Foreign Ministry official on assignment at the Defense Ministry.

The Defense Ministry confirmed its premises had been searched but gave no other details.

"It is not yet clear what is behind this," Defense Minister Ursula von der Leyen told the Berliner Zeitung newspaper, in an excerpt of Thursday's edition.

Merkel has already said the arrest last week of a low-level official of Germany's foreign intelligence agency, known as the BND, for spying for the United States would, if confirmed, be a "serious case". But she also says it will not affect transatlantic free trade talks.

The chancellor faces political fallout for not criticizing President Barack Obama sufficiently for alleged surveillance in Germany by the US National Security Agency, which targeted her mobile phone for eavesdropping. The new cases put further pressure on Merkel to react.

Yasmin Fahimi, general secretary of the Social Democrats (SPD) who share power with Merkel's conservatives, urged the "immediate removal of embassy staff involved and the immediate cessation of all other espionage in our country".

Von der Leyen, who is from Merkel's party, said the NSA case had "shaken confidence" in the United States and it had to be made clear to the intelligence community that "not everything that is possible is politically acceptable".

NTJ/NJF